Two-wire automatic telephone system.



Y T. G. MARTIN; TWO WIRE AUTOMATIC TELEBHONE SYSTEM.

APPLICATION FILED MAR. 2l. |908.l RENVEWED APR- 12.I9IT.4

Patented D.v4,1917.

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TWD WIRE AUTOMATIC TELEPHONE SYSTEM. i APPLICATION FILED Mmm, 190s. RENEWED mi. 12.1911.

1,249,159. I Patented' nw 4,1917.

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my invention consists in matters herein-V UNITED sTATEs PATENT oEEIoE.

TALBOT G. MA'RTIN, OF CHICAGO, ILLINOIS ASSIGNOR, BY MESNE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC COMPANY, 0F CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TWO-WIRE .AUTOMATIC TELEPHONE SYSTEM.

Application led March 21, 1908, Serial N o. 422,462. Renewed April 12, 1917.

.To all whom 'it may concern.'

Be it known that I, TALBOT G. MARTIN, a citizen of the United States of America, and 'resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in Two-Wire Automatic T elephone Systems, of which the following is a specification.

My invention relates tortelephone systems in general, but more particularly to automatic or semi-automatic telephone exchange systems, and especially to systems in which the subscribers lines are free froml operating grounds outside of the exchange or central station, these being ordinarily known as two-'wire systems.

Objects of my `invention are to provide a two-wire system in which automatic partyliuc service can be given the subscribers thereof; to provide a two-wire automatic telephone exchange system in which subscribers on the same line signal cach other bymeans of push-buttons at their respective stations, while a called subscriber on another line is signaled automatically from the eX- change or central station; to'provide a twowiie automatic telephone exchange system in which the connectors will lock on busy called lines, without closing the callingline in connection therewith, the calling subscriber being at the same time given a busy signal; to provide a two-wire automatic tel-- ephone exchange system in which provision is made for enabling a party-line subscriber to call back on his own line, in order to establish telephonie communication with another subscriber on the same line; and to provide certain novel details and features of improvement and combinations tending to `increase the general eiiiciency and serviceability of a telephone exchange system of this particular character.

To the foregoing and vother useful ends,

after set forth and claimed.

In the accompanying drawings, Figure 1 is a diagrammatic representation of partyline equipment embodying the principles of my invention. The substations A and A]L are allotted to a common line which terminates at the central ollice in the -line switch C. At D is represented the master switch for `controllin the line switches of the group of whic the switch C is a member.

Specification of Letters Patent.

Patented Dec. 4, 191 7.

Serial No. 161,680.

Fig. 4 represents more fully the line` switch C and the controlling master switch Fig. 5 is a detail view of the master switch bank Fig. 6 represents dia grammatically the arrangement of the lines by means of which the different substations may besignaled selectively.

In this system each subscribers line is, of course, provided with a line 'switch similar. to the line switch C, and usually. onehundred of these form a grou l" Also, to each such group there is allotte a grou of first-selector switches in common. The rstselector switches may first select any one of second-selectors, and then some one of the selected group which may be idle. The seoond-sclcctor switches may in turn b operated to first select any one of a number of groups of connector switches, and then some one ofthe connectors of the selected group which mayY he idle. Each group of connector-switches is also arranged to take care of one-humlred subscribersthat is, if any subscriber in thc system wants to call another subscriber he must, through the medium of thcl y first selector and second-selector switches, pick out a certain group of connectors, any one of the connectors of which group is capable of establishing the final connection with the desired subscriber in a particular hundred. i' i The substations may be of any suitable or approved type. As shown, it will be seen that substation A is somewhat-different from -theY usual automatic substation, said substation A being arranged and modified in turn be operated to to operate in connection with a two-wirea number of groups ofv 6, transmitter 7, condenser 8, ringer 9 an i -is shown at Q (Fig. 4).

1m ulse wheel 10 which has the usual impulse teeth 11. The impulse wheel 10 is secured to the shaft 12, to which shaft there is also secured the dial (not shown). When the dial is turned, the impulse teeth 11 are adapted to engage the cam 13 upon the end of the spring 14 and thereby carry the latter out of engagement with the spring 15. Upon ,the switch-hook 3 is secured the cam 16 which, when the switch-hook .is up, permits the springs 17 and 18 to engage, thereby bridging across the subscribers line conductors 19 and 20 the primary circuit including the transmitter 7 in series with the primary winding 5; but when the switchhook is lowered the spring 17 is carried out of engagement with the spring 18 and into engagement with the spring 18C, whereby the ringer 9 in series with the condenser 8 is `bridged across the line conductors 19 and 20 instead, Furthermore, the substation A is Aprovided with a signaling button 5 which, when pressed, disengages the springs aand 7 a, whereby the short-circuit or shunt around the resistance coil 8UL is removed.

The line switch C (Fig` 4) comprises a plunger 21, plunger arm 22, trip magnet 23, and switch-release magnet 24, all of which are assembled upon a suitable base or frame (not shown). The said switch-release magnet is provided with an armature 25 that is pivoted on a pin 26 which rises from the base of the switch. The said armature carries pivotally secured on its end a second armature 27 that is controlled by the trip magnet 23. The pin 28 about which the armature 27 moves is carried on the end of the-armature 25. The plunger 21 is pivotally secured by the pin 29 to the plunger arm 22, which latter is in turn pivoted by a pin 30 that rises froml the switch frame (not shown). The lug 31 may be stamped from the frame and is provided as 'a stop for the armature 25. Upon the armature 27 is secured the member 32 which is adapted to normally engage the end 33 of the plunger arm 22. Furthermore, the said line switch is provided with a bank of terminals, usually ten in number, but only one of 'which The said terminal Q .is shown turned from its true position with respect .to the swing of the plunger 21, and the bushing 34 is correspondingly turned,

all for the purpose of making the illustration clearer. The terminal Q comprises the springs 35 and 36, 37 and 38, 3S) and 40, and 41 and 42. These springs are normally dis- 65 connected from each other, but are driven into contact, as shown in the drawings, when the )lunger 21 engages the b ank terminal Q. hen the plunger 21 disengages from the bank terminal Q, the said plunger may take one of two positions relative to the plunger shaft 43-that is, the lunger may return to either locked or sli ing engagement with the shaft 43. When the plunger 21 is in locked engagement with the plunger shaft 43, the notch 44 is in engagement with the flange or web4 45 of the shaft 43; and when in sliding engagement the fan-like tailpiece 46 restsin the position shown by the dotted lines in Fig. 4-that is, when the plunger shaft is operated the plunger 21 is not carried along with the locked plungers, but remains in the dotted position, the plunger shaft sliding upon the edge of the tail-plece 46, The general operation of the switch `is as follows: The trip magnet 23 is energized when the receiver is removed from the switch-hook and the armature 27 is attracted against the magnet cores. When the armature 27 is attracted the catch 32 slides out of contact with the end 33 of the plunger arm 22, and the said plunger arm 22, owin to the tension o-f the spring 47, moves a out the pin 30 and thrusts the plunger 21 into the bank terminal Q; and when the trip ma iet again denergizes, the trip armature 27 alls against the end 33 of the plunger arm 22, as shown. Furthermore, when the line switch operates, and the plunger 21 is thrust onto the bank terminal Q, the shaft 43 is advanced one step, as will be explained, to carry the locked plungers opposite the next idle trunk-line. The switch is restored by the release magnet 24, on whose energization the armature 25 is attracted, and accordingly the trip armature 27 is moved up* wardly until the catch 32 slides over the end 33; then when the release magnet 24 becomes denergized the armature 25 returns to normal position and remains at rest against the stop 31. Furthermore, since the p unger arm 22 is now in engagement with the catch 32 of the armature 27, the said plunger arm is also moved about the pin 30, whereby the plunger 21 is moved from the terminal Q. Also, since the plunger shaft has advanced one step, the tail-piece 46 of the plunger 21 comes to rest in the position shown by the dotted lilies, in sliding engagement with the plunger shaft 43; and as the said plunger shaft advances each time an idle trunk is seized, the plunger 2l is not advanced, but remains in this posisaid master switch also `prising a plurality of individual contact when the web of the said shaft oi er which the slot 44 normally rides arrives at the position in which the plunger 21 was originally releasede-that is, the plun er passes into locked engagement with the s aft when the slot 44 slips over the web of said shaft. From thence on .the plunger 21 is carried in locked engagement by the shaft 43 until it is again plunged in when another call is made. But if after the plungel` is released, and before the shaft 43 returns to pick up said plunger, the switch C is again operated, the plunger 21 again engages the same terminal Q. The bridge-cut-off relay 48 is' provided for controlling the. springs 49, 50, 51 and 52, and, upon energizing, operates to shift the springs 49 and 51 out of engagement with the springs 50 and 52. When the springs are thus operated the line switch C is isconnectcd from the substation line conductors. y l

The master switch D, which may be of an \r suitable or approved type, is provided for operating the plunger shaft 43 and for controlling certain circuits that will be disclosed hereinafter. It comprises the following details: A motor magnet 53 for operating the ratchet wheel 54, which latter is designed for operating the plunger shaft 43 through the medium of the cam 55, and a differential relay 56 for controlling the energizing circuit of the motor magnet 53. The

has a bank O comsegnients a and a common metallic segment 57, as shown in Fig. 4. The Wiper 58 is adapted to remain in constant engagement with the bank O, and to at all times, except when the wiper is assing from the extreme left contact 59 to t e eXtreme right contact 60, maintain some one of the segments a in electrical connection with the common segment 57. As shown in Fig. 5 the individual segments a are separated from the common segment 57 by the insulating strip 61. The spring 62 is provided so that when the Wiper is carried tothe contact on the extreme right, the upper part of the wiper 58 slides on the guide spring 62, thus preventing the Wiper from placing any of the individual segmentsa in contact with the common segment 57, whereby some interference might be causedwith the master switch. The wiper 58 is operated in a stepby-step manner by the ratchet Wheel 54, through the medium of the cam member 55 rigidly secured to the said wiper 58, and is adapted to successively engage the pins 63, 64, 65 and 66 upon the said ratchet Wheel 54. The

motor magnet 53 is provided with an armature 67 upon the end of which there is suitably secured a pawl 68. Each time that the said magnet is energized, the armature 67 is attracted against the magnet cores, and

the pawl 68 engages a tooth on the ratchet wheel 54, thereby advancing the latter one step. It will be seen, therefore, that as the ratchet wheel 54 advances, the wiper 58 advances step by step from right to left; and when the pin 63, for instance, clears the rain 55, the retraeting spring 69 then restores the wiper 58 to its first position at the right of the bank and in engagement with the firsl segment (it). 'lhe said motor magnet is provided with a couple of interrupter springs 70 and 71 that are included in the energizing circuit of the said niotor magnet', which energizing circuit also coniprises the springs 72 and 73 controlled by the differential relay 56. 'l`herefore, whenever the di'erental relay is energized the springs 72 and 73 are pressed into contact, and the motor magnet operates step by step as long as the differential relay 56 remains energized. I `urther1norc, it is sumed that the terminal Q of the line switch C is thc first terminal ot' the Vline switch bank. While in normal locking engagement with the shaft 43, the plunger 21 is retained in front of Said terminal by the plunger shaft 43, whenever the master switch wiper 58 is in engagement with the bank segment 60; but as the motor magnet 53 advances the wiper` 58 onto the secondA segment 74, the said plunger and all idle plungers similarly engaging the shaft 43 are carried opposite the next terminal of the line switch bank. It should be noted that in each line switch'bank all of the springs 35 are permanently connected and may be made of one common piece. The springs 36, however, are individua1-that is, there is one separate and distinct spring for every bank set Q, there being ten in the bank. The springs 37, 39 and 41, like the springs 35, are all common, and the springs 38, 40 and 42, like the springs 36, are individual. For every bank terminal Q there is a trunk-line of three conductors 75, 76 and 77 leading to Ia selector; and there is also a normal trunklinc comprising the conductors 78, 79 and 80 leading to the connector banks. The subscribers line conductors 19 and 20 terminate in the springs 35 and 37 which, as has been stated, are common springs. When the subscriber operates the line switch C, andthe plunger 21 engages the terminal Q, the subscribers line conductors 19 and 20 are eX- tended to the vertical and rotary trunk conductors and 76, thence through the windings 21a and 22a of the relay 23a (as shown in Fig. 1) to the'first-selector switch E.

The first-selector switch shown at E is of the general type described-in lUnited States Letters Patent No. 815,321, granted March 13, 1906, to Keith, Erickson & Erickson, and, as shown, is modified toadapt it to operate in connection with a two-wire system. It embodies among other details the following features :v The switch shaft (not shown) earries the. negative. and positive line wipers 81 and 82, and the private wiper 83. The side switch is well known and comprises the side switch wipers` 81, 85, and 87 which may be designated as the vertical, rotary and private side switch wipers, and the rotary magnet wiper, respectively. The side switch is under the control ofthe private magnet 88, and when the side switch is in normal or first position the wipers 81, 85, 86 and 87 occupy the contact points 89, 90, 91 and 92, respectively. In the second position the wipers rest on the contact points 93, 91, 95 and96, respectively; and when in third position the contact points 9T, 98, 09 and 100 are engaged by their respective wijliers. The windin s of the usual vertical ano rotary line re ays are, in this case, combined into one double-wcnind relay 101 comprising the winding 102 which is connected with the battery lead 103, and also with the vertical trunk-line conductor, when the side switch wiper 84. is in first or second position. The second winding 101 is connected to ground, and also to the rotary trunk-line conductor, when the side switch wiper is in lirst or second position. Through the medium of this double-wound relay, and while the side switch is iii-first position, the subscriber controls the vertical magnet 105 which operates to raise the switch shaft and wipers 81, 82 and 83 vertically. This line relay 101 also controls the private lnagnet relay 100, 'which latter in turn controls the private magnet 88. As usual, the private magnet controls the side switch. While the side switch is in second position the rotary magnet 10T, which operates to arry the switch shaft and wipers 81. 82 and 83 in a rotary direction, is energized. The release magnet 108 provides means for restoring the selector switch to normal position. Upon the switch shaft which carries the wipers 81, 82 and 83 there is mounted the arm 109 which, whenthe shaft is raised one or more steps, permits the spring 110 to engage the'contact point 111, whereby the'release magnet 108 is connected to the battery lead. The release relay 112 is provided for closing the energizing circuit of the release magnet 108 after the switch is operated. The back-release relay 113 is provided for opening the energizing circuit through the release magnet 21 of the line switch. The relays 106, 112 and 113 are slow-acting relays-that is, they are so provided witha copper shield that when energized and the energizing circuit then .broken the said relays remain in an operated position for a moment or so. In other words, they do not instantly return to normal position after the energizing circuit is broken.

The second-selector l? (Fig. 2) is'similar to the first-selector E, and is provided with the usual doublcwound line relay 11-1 ha ving the windings 115 and 116 connected with the vertical and rotary side switch Wipers 117 and 118 in the same manner in which the windings of the relay 101 of the `selector switch E are connected with their vertical and rotary side switch wipers. Since like parts are similarly represented, the rotary magnet 119 and the vertical magnet 120 will be recognized and understood. The release magnet 121 is operated in the same manner `in connection with the switch F that the release. magnet 108 is operated in connection with the switch E. The private magnet 122 is controlled by the private magnet relay 123. The release relay 121 of 'the second-selector switch F performs the same function inconnect-ion with this switch that the release relay 112 and the baclereleasc relay 113 perform in connection with the first-selector switch llfthat is, the springs controlled by the relays7l'1l2 and 113 are so arranged in the second-selector switch F that they are controlled by the one relay 124. In the switch F the relays 123 and 124 are so arranged that they dcnergize slowly, the same as the relays 106, 112 and 113 of the selector switch E.

The connector switch H is a modified form of the connector switch disclosed in United States Letters Patent No. 815,176, granted li'Iarch 13, 1900, to Keith, Erickson & Erickson. The connector switch shaft (not shown), like the switch shaft ofthe selector, earries the line wipers 125 and 126 and a private' wiper 127. The connector switch is also controlled by the calling subscriber through the medium of a doublewound line relay 128. The line relay 128 is provided with the windings 129 and 130. One terminal of the winding 129 is connected to the batteryY lead, while the other terminal is connected with the vertical trunlr. line conductor. The winding 130 is connected with ground andl also with the rotary trunk-line conductor. This line relay 128 directly controls the vertical magnet 131. The purpose of the vertical magnet 131 is to give the shaft4 and shaft wipers a vertical motion, and the rotary magnet 132 imparts to the shaft and shaft wipers a rotary or circular' motion. The connector switch is also provided with the slowacting release relay 133 which is the same as the release relay 124: of the second-selector switch. As usual, the private magnet relay 134 controls the private magnet 135, which latter' controls the side switch wipers 13o', 137, 138, 139 and 140. The back-bridge relay 141, comprisinp4 the windings 142 and 143, provides the means whereby the called subscriber is .furnished with battery current for talking purposes. -As here shown, my connector switch is of the automatic ringing typethat is, a signaling of the called subscriber is not dependent upon the calling subscriber pressing a signahng button when he calls a line not his own; for as soon as connection i". established with the desired line the interrupter 144 intermittently closes an energizin circuit through the ringer relay145, w ereby the terminals of the ringer generator I are intermittently bridged across the normal conductors of the called line. The relay 146 is so arranged that if a busy line is called the connector side switch i. ockecl in second position, and the calling subscriber is iven-the busy-signal. The means whereby t e connector switch may be restored to normal position is provided by the usual release magnet 133EL which, when the connector switch shaft is raised one or more steps, is connected to the battery lead through the, normal springs 131'l and 1322. By means of the condensers 147 and 148 the circuit through the connector switch is divided into two sections. The busy-signaling apparatus J comprises the interrupter 149 in series with the winding 150 of the induction-coil 151. The winding 152 is ,connected with the spring 153, and when the relay 146 energizes, as lwill be explained. the busy-signaling apparatus is connected with thc connector or side switch wiper 136.

The operation of the system may be more clearly understood from an explanation of its operation in establishing a connection. It will be assumed that the subscriber at substation A Wishes to call the subscriber' at substation A2, to which latter is allotted the number 2220. To call the number 2220 (substation A2, F ig. 2) the subscriber at substation A (Fig. 1) removes his receiver from the switch-hook, and operates the calling device for each digit, in the well-known mannerthat is, when'the receiver is removed from the switch-hook a preliminary .impulse provides an energizing circuit for the trip magnet 23 of the linel switch C, whereby the line switch (l is operated to seize an idle and waiting or preselected trunkline leading to a first-selector switch.

The dial is turned for the first digit, andY uponreturning to normal position operates the frst-selector switch to establish connection with an idle trunk-line leading-to a Second-selector switch. In a similar manner the dial, upon returning to normal positiony for the second digit,- operates the secondselector switch l" to establish connection with an idle trunk-liuc leading to a con nector switch. The imliulses delivered by the dial for the last two digits are directed toward the connector Il, which latter opcrates'to place the'sbaft wipers in connection with the contacts corresponding to thc`desired subscriber. The preliminary impulse for energizing the trip magnet 23 occurs when the receiver 2 is removed from the switch-hook 3 and the cam-arm 16 permits the spring 17 .to engage tbe spring 18, thereby removing the ringer from across the line and bringing the primary circuit instead. When the primary circuit is thus bridged across the line, the energizing circuit for the trip magnet 23 is completed and extends from ground G (Fi 4) through the trip magnet 23, throng the springs 50 and 49, conductori155 to the rotary llne conductor 20 (Fig. 1), resistance coil 8a and springs 6 and 7L in multiple, through the springs 17 and 18, impulse springs 15 and 14, primary windin 5, transmitter 7 to the vertical line con uctor 19, thence through the conductor 156 (Fig. 4), springs 51 and 52, through the resistance coil 154 to the battery lead 103, thence through battery B to ground G. As soon as the trip magnet 23 energizes, the armature 27 is attracted and the plunger 21 is liberated and thrust into the bank terminal Q by the spring 47, assuming that the plunger 21 is opposite the terminal Q atthe time. VVh'en the plunger 21 engages the bank terminal Q, an energizing circuit is established through the motor magnet relay 56, which in turn operates to close an energizing circuit through the Imotor magnet 53 of the master switch D. The motor magnet then operates to advance all idle plungers that are in locking engagement with the shaft 43 opposite the nekt idle bank terminal similar to the terminal Q. The circuit through the relay extends from ground Gr2 through the wi ing 158 of the relay 56 to the common segment 57, thence through the wiper 58, through the Contact 60, conductor 159, bank terminal springs 42 and 41, through the Wwinding of the release magnet 24 to the battery lead 103, thence` through battery B to ground G. Although this circuit includes;

the release magnet 24, the said magnet does not operatively energize, since the winding of the relay 56 is of a high resistance, while the winding ,of the release magnet 24 'is comparatively low. The relay 56, upon energizing, operates to' place the sprlngs 72 and 73 in contact, whereby a circuit is complated through the motor magnet 53, said circuit'extcnding fromy ground G3 through the springs 72 and 73, motor magnet springs and 71, through the winding of the motor magnet` 53 to the battery lead 103, thence-- The motor' in normal locked position with the shaft 43, l.-1230 through the relay energized, as will be opposite another terminal similar to the terminal Q, assuming the next succeeding trunk is idle. Conse ucntly, the wiper arm 58 is carried from t e contact )oint 60 (which corresponds to the termina Q) to the contact point 74, which latter corresponds to the terminal before which the advanced idle plungers are now resting. Suppose that nine subscribers have called, and that the master switch has 4thus operated nino steps, carrying the wiper 58 to the last contact point 59. Now, when the motor magnet 53 operates for the next step, when the tenth subscriber calls, the wiper 58 passes back and drops into engagement with the contact point 60. If the rst trunk is still busy the Wiper 58 linds a battery potential on the contact 60, and an energizing circuit is established through the diierential relay 56, which in turn operates to close an energiz ing circuit through the motor magnet 53. The current through the said relay 56 Hows from the said Contact 00 through the wiper 58 to the common segment 57, and throuUh the winding 158 of the differential relay o6 to ground G2.. When this relay energizes it operates to close the circuit through the motor magnet 53, and the motor magnet then operates, as previously explained, to rotate the ratchet wheel 54 one step, and the masterswitch bank wiper 58 one step also and into engagement with the second segment 74. When thus advanced one step the plunger shaft 43 carries all idle plungers that are in locking engagement with said shaft opposite the second bank terminal, as perviously explained. If there should still be a uarding potential at the bank segment 4, the differential relay 56 will remain energized, whereby the energizing circuit through thc motor magnet 53 is again completed when the motor magnet springs and 71 again engage, and as a result the motor magnet 53 is again operated, whereby the plunger shaft and the master switch wiper 58 are advanced another step. This process continues as long as the wiper 58 continues to find segments with guarding lpotentials. As soon as an idle segment is found, however, the energizing circuit 56 is broken, .at which time thcsaid relay in turn breaks the energizing circuit for the motor magnet 53', until the next subscriber makes a call. At the instan'tthat the plunger 21 enters theI bank terminal Q the follow-ing springs are pressed into contact: 35 and 36, -3.7 and 38, 30 and 40, and 41 and 42. ,'lheeugagemeut of the springs 39 and 40 closes a'c1c|iit through thecut-ofi" relay 48 extending from ground G through the springs 1G and 1T". springs 18" and 19" of the relay 23" p whirh is now explainet-l) conductor 157, through the springs t0-and 39, conductor 160, relay 48 tothe battery lead 103,

thence through battery B to ground G. The said relay, upon energizing, operates to carry the springs 49 and 51 out of engagement With the springs 50 and 52. When thesc springs discngage, the resistance coil 154 is disconnected from the vertical line conductor 19, and thc trip magnet 23 is disconnected from the rotary line conductor 20. The engagement of the bank springs 39 and 40 also establishes a guarding potential by Way of the normal conductor to the connector private bank contacts corresponding to the line that terminates in the line switch C, to prevent any subscriber from calling the said lineafter the calling subscriber at sub! station A. removes his receiver preparatory to making a call, as explained. Also, the closure of connection between the springs 41 and 42 establishes a guarding potential at the master-switch bank Contact GO, over the following circuit: from battery B to the battery lead 103, thence through the Winding of the release magnet 24, through the springs 41 and 4Q, conductor 159 to the said Contact point 60. It will be understood that the bank terminal Q, being the first bank terminal of the line switch bank, corresponds to the first segment 60 of the master switch bank O and, therefore, to the trunk-line the conductors 75, 7'6 and 77 of which terminate in the first-selector switch E. This uarding potential protects the seized trun conductors 75, 76 and Ti' from being seized by other plungers, as already explained. The closure of connection between the springs 35 and 36 extends the calling subseribers vertical line conductor 19 to the vertical trunk conductor 75 and the side switch wiper 84 of the first-selector switch E. The closure of contact between the springs 37 and 38 in a similar manner extends the subscribers rotary line conductor 20 to the rotary trunk conductor 76 and to the side switch wiper 85 vof the selector E. The subscriber has thus established connection with the next selector switch, which is now operated by the impulses that are delivered when the dial returns to normal position for the first digit. When the Subscribers line conductors 19 and 20 are thus extended to the First-selector switch E, an energizing circuit is established through the line relay 101 extending from ground (il5 through the winding 104 to the contact point 90, side switch wiper 85, winding 2:2 of the relay 23, trunk conductor 76. through the bank springs 88 and 37'to thc rotary line conductor 20, throughfthe springs 17 and 18, impulse springs 15 and 14. primary winding 5. transmitter 7to the vertical line conductor 19, through thc bank springs 35 and 3G, trunk conductor 75, winding *21'* of thc relay '23". side switch wiper 84. Contact point 89, through the winding 102 to the battery lead 103, thence through battery B to ground G. Both windings of the relay 23 being included in this circuit, the said relay operatively euergizes to place the springs 19 and 1Sa in contact, thereby providing the guarding potential for protecting-the line and completing an energizing circuit for the bridge-cutoff relay 1S, as explained. The relay 101. upon energizing, operates to place the springs 161 and 16'2 in contact, whereby an energizing ci'rcuit is established through the release relay 112 extending from ground G through the springs 161 and 162, relay 112 to the battery lead 103, thence through battery B to ground G. The release relay 112, upon energizing. operates to carry the spring 163 out of engagement with the spring 16-1 and into yengagement with the spring 165. This is the condition of the first-selector switch E when the subscriber operates the dial for the first digit. The first digit being 2, the impulse spring 14 is twice carried out of engagement with the impulse spring 15. As a. result the energizing circuit through the line relay 101 is broken twice, and the spring 161 comes into contact with the spring 166 twice. a After the. two impulses are thus transmitted', the line relay 101 again energizes and carries the spring 161 into contactl with the spring 16:2. As previously ex plained, fthe relay 11i! is slo\v-acting--tliat is, slow tmdeinergize; and when -its energizing' circuit Iis momentarily broken, during the verticalimpulses just delivered, the said relay does not deneigize. but remains in an operatedy position with the spring. 163 in contact with the spring 165- Then, when the srpring 161 engages the spi-ing 166, two

impijilses are transmitted to the vertical magnet 105 from ground G through the springs161 and 166 to the springs 163 and 165, through the private, magnet relay 106, through the winding of the vertical magnet 105, contact point 0:2. side switch wiper 87 to the battery lead-103, thence through batteryB to ground G. 'l`he impulses being transmitted, the vertical magnet 105 is thereby energized twice, and the shaft. wipers are given two vertical steps in the, well-known manner. 1t will he seen that the private. magnet relay 106 is included in the energizing circuit of the vertical magnet 105. 'lhis relay also energizes, lult being a slowaeting relay it energizes on the f irrst iinpulse and remains so until all the impulses a re transmitted. 'lhis relay, upon energizing, operates to close the springs 167 and 10S in contact, whereby an energizing circuit. is established through the private magnet 88. This circuit extends ground G through the springs 167 and 168, private magnet SS to the battery lead 103, thence through battery Il to ground G. The private magnet relay 10t'i'deiiiiergizes after the last vertical impulse., since its energizing from .circuit is no longer maintained after the springs 161 and 166 disengage. Hence, the said relay denergizes, permitting the springs 16T and 168 to disengage, whereby ilie energizing circuit through the priva@ magnet SS is in turn broken, which private magnet now deneigizes and permits the side switch to pass from first to second position, permitting the side switch wipers 86 and 87 to engage the contact points 95 and 96, respectively' 'Lhe closure of contact between the side switch wiper 87 and the contact point 06 sets up an energizing circuit for the rotary magnet 107 from'ground G5 through the interruptor spring 169, through the winding of the rotary magnet 107, contaet. point 96, side switch wiper 87 to the battery lead 103, thence through battery B to ground G. The said rotary magnet then operates to rotate the'shaft wipers 81, 82 and S3 of the selector E into engagement with the rst Contact of the second level of the selector banks, from which Contact it is assumed Vthe trunk-line conductors 170, 171 and 17;) lead to the seeondseleetor switch l?. lt' the tirs-t trunk-line is busy, however, and the wipers have to pam over busy trunklines. then as soon as the private wiper S3 engages the first private bank contact, the private magnet 8S again energizes, locking the side switch in second position. The energizing circuit for said private magnet extends from the. grounded terminal G of the battery li through an occupying switch (not'shown). through the private wiper S3, thence tliioughthe conductor 173 to the side switch wiper S6, Contact point 95, through the winding ot the private magnet SS to the battery lead 103` thence through battery B to ground G. The private magnet S8, upon thus becoming energized, locks the side switch wiper ST in engagement with the contact point 96, whereby the rotary magnet 10T will be energized step by step until the wipers are carried beyond the last busy trunk-line. .\t the instant that the private wiper leaves the last busy Contact point the energizing circuit through the private niagnet SS is destroyed, and as a result the `selector side switch passes to third position. lf, however, there are. no busy trunk-lines. the private magnet 8S releases the side switch to third position as `soon as the wipers are carried into engagement with the first trunkline. As soon as the side switch passes to third position, as stated. the subscri ier`sl line conductors` 19 and .20 are extended to the conductors 170 and 171, which, in this case, it is assumed lead to the second-selector switch F. The extending of the line occurs, of Coulee, as soon as the side switch wipers Si and S5 engage the contact. points 97 and 0S, respectively. When the subscribers line. conductors are thus extended to the selector switch F an energizing circuit is estahlished through the line relay 114, in the same manner in which the energizing circuit-'was established through the line relay 101 of the selector E when the subscriber-s lineeonductors 19 and 2O were extended through the line switch bank to the trunk conductors and 76. The relay 1111, upon energizing, operates to shift the spring 174 from the spring 175 to the spring 176. Then the springs 174 and 176 engage, an energizing circuit is established through thc release relay 124. This circuit extends from ground G1 through the springs 171- and-176, through the relay 121 to the battery lead 103, thence through battery B to ground G. The relay, upon energizing, operates to shift the spring 177 from the spring 17S to the sprin 179, and the springs 18() and 181 are also c osed in Contact. This operation of the second-selector switchF occurs at the instant that the side switch wipers 84 and 85 of the selector switch E pass to third position and extend the subscriber-s line conductors 19 and 20 to the second-selector switch F. when the secoml-sclector switch, therefore, thus operates, a guarding potential is established at the private wiper 83 for protecting the seized trunk-line conductors 171 and 172 against seizure by another calling tirstselector. This guarding potential extends from ground G to the contact point 182, side switch wiper 183,'through the springs 181 and 180, conductor 172 to the Contact engaged by the private wiper 83. Furthern'iore. when the first-selector switch E operates and the side `switch passes to third position. a new energizing circuit is established through the release relay 112. This energizing circuit. extends from ground G at the selector switch F through the springs 181 and 180, conductor 172, shaft wiper S3, conductor 173, through thel side switch wiper S6, contact point 99, relay 112, through the hatter7 load 10?, thence through battery B to groinid (ir. The relay 112 thus remains in an operated position with the. spring 103 in engagement with the spring 165, but the line relay 101 returns to norlnal position when the side. switch wipers 84 and 85 engage the contact points 97 and 9S, respectively. .The energizing circuit through the line relay 114 extends from ground (1" through the winding 11G to the side, switch wiper 118, thence. througl'l the. conductor 171, winding 22, rouduetor 76 and line, conductor 2t), through the primalyr circuit of the, stilistation. through .the vertical line conductor 19. thence through the. trunk conductor 75, winding 2l, conductor 170, side switch wiper 117, through the winding 115'` of the relay 1t--tto the battery lead 103, thence. through battery B to ground (l. WVhen the dial returns to uorlnal position 'for the .st-rond digit. 2, this circuit through the. line rela)-r 1lfl is interrupted twice, when the i|n pulse springr 14 is carried out of engagement with the spring 15 by the impulse teeth on the wheel 10. The circuit being interrupted twice, said relay 114 momentarily denergizes twice, thus permitting thc spring 174 to engagev the spring 175 a like number of tunes. whereby an energizing circuit is twice completed through thc vertical magnet 120 extending trom ground G7 to the springs 174 and 17:3, springs 177 and 179, through the winding of' the private magnetl relay 123, through the winding ol the, vertical ma net 120, contact point 184, side switch wiper 185 to the battery lead 103, and through battery i to ground (l. The private magnet relay .123 being included in this circuit energizes, and since it is a slow-acting relay it remains in an operated position until the last Ver* tical impulse trruisrnitted, and the relay 11-'1 reniains energized with the spring 174 in contact'. with the spring 176, whereby the circuit. through the private magnet relay and the vert-ical magnet 120 ren'lains open. \\'hen the relay 123 energizcs, the springs ISG and 187 are pressed into contact, thereby causing an energizing current to flow through the private magnet 122, the circuit extending from ground G7 through the springs 187 and 186, through the winding of the private magnet 122 to the battery lead 1053, thence through battery B to ground G. Then the relay 123 denergizes and breaks the energizing circuit through the privatel magnet 122, the private magnet also detnergizes and permits the side switch to pass trom first to second position. than the .side switch wiper 185 passes to second position and into engagement with the contact point 188, an energizing circuit. is established through the rotary n'iagnet 119, which latter now operates, as explained in connection with the rotary magnet 107 ot the Selector switch E,

to select au idle, trunk-line leading to the connector switch. After the switch comes to rest, with the side switch in third position, the shaft wipers 189, 190 and 191 are in engagement w1th the trunk conductors 192, 193 and 19d, respectively, which lead to the-connector switch H (Fig. 2). At the instant that the side Switch wipers 117 and 118 pass to third position, in engagement with the, contact points 195 and 196, the. subv scribers line conductors are extended to the connector switch H and an energizing eir cuit is established through the line relay 128 and the differential relay 23, in the same manner in which the energizing eirruit was established through the line relay 114 of the selector switch l" when the side switch wipers of the first-selector passed to third position. The energizing circuitv through the line relay 12S extends 'troni ground G through the, winding ltl` trunk conductors 1921i, 171 and 7G to the line con- 'iso the spring 1901l from the spring 197 to the' spring 198, whereby an energizing 'circuit is established through the release relay 133 extending from ground G11 through the springs 196a and 198, relay 133 to the batf tery lead 103, thence through battery B to ground Gr. l/Vhen the. relay 133 energizes,

. the spring 199 is shifted out of contact with the spring 200 and into contact with. the spring 201, and the spring 202 is shifted into engagement with the spring 203. This .primary operation of the connector relays 123 and 133 occurs` at the instant that the side switch wipers 117 and 118 of the selector F pass to third position and extend the subscribers line conductors to the connector H, The engagement of the springs 203 and 202 establishes a guarding potential for protecting the trunlcline conductors 192, 193 and 194 against seizure by another line and second-selector. This potential extends rom ground G11 to theside switch wiper 139, springs 203 and 202, conductor 194 to the private bank Contact engaged by the shaft wiper 191. -Furthemore, when the side switch of the seccid-selector jFpasses to third position a new energizing circuit is established through the release relay 124, said circuit extending from ground G11 at the connectorl switch to the conductor 194, through the shaft wiper 191, side switch wiper 204, conductor 205, through the release relay 124 to the battery lead 103, thence through battery B to ground G. Also, this same guarding potential established at the contact engaged by the private shaft wiper 191 is extended to the private bank contact engaged by the shaft wiper 83 of the iirstselector' E, when the side switch of the second-selector F passes to third position. The path over which this potential extends is as follows: from ground G11 at the connector switch-H (Fig. 2) through the side switch wiper 139, springs 203 and 202, conductor 194, shaft wiperi191, side switch wiper 204, conductor 205, contact point 20G, side switch wiper 183, springs 181 and 180, conductor 172 to the bank contact engaged by the pri vate wiper-83 of the selector switch E. The operation of the dial for the last two digits afects the connector' switch, and when the dial is operated for the third digit 2 the impulse spring 14 is twice carried out of engagement with the spring 15, thereby inomentarily dcnergizing the line relay 128 twice, whereby the spring 1961 twice engages the spring 197, thus sending two impulses to the vertical magnet 131 from ground G11 through the springs 196 and 197, springs 199 and 201, through the vertical magnet 131, contact point 207, side switch wiper 140, private magnet relay 134 to the battery lead 103, thence through battery B to ground Gr. The private magnet relay 134 energizes when the first impulse is delivered, and since the said relay is slowacting it remains in an .operated position until all the vertical impulses are sent. The vertical magnet, upon being energized, operates one step at a time to carry the shaft wipers 125, 126 and 127 two steps to a point opposite the second level. The rela-y 134,` upon energizing, shifts the spring 209 out of engagement with the spring 210'and into engagement with the spring 211; also, the spring 212 is shifted out of engagement with the spring 211. When the springs 209 and 211 engage, an energizing circuit is established through the private magnet 135 from ground G11 through the springs 211 and 209, private magnet 135 to the battery lead 103, thence through battery B to ground Gr. The rela'y 134, being a slow-acting relay, remains in an operated position while the vertical impulses are being sent; but after all the impulses are delivered, and the line relay 128 returns to its operated position, the circuit through the relay 134 becomes broken, thus permitting the springs 212 and 209 to return to normal position.

When the springs 209 and 211 disengage, the circuit -through the private magnet 135 becomes broken, whereby the said magnet denergizes, permitting the side switch to ass from first to second position. The calling subscriber now operates the calling device for the last digit 0, thereby transmitting ten impulses and operating theline relay 128 ten times. Each time that the line relay springs 196a and 197 engage, an4- energizing circuit is established through the rotary magnet 132 from ground G11 through the said springs 193a and 197 and through "the springs 199 and 201, rotary magnet 132 and locking-relay springs 211'1 and ,212 to the contact point 213, thence through the side switch wiper 140, and through the pri. vate magnet 134 to the battery lead 103, thence through battery B to ground G. Again the private magnet relay energizes, as in the previous case, remaining so until all the impulses are transmitted, thereby retaining the private magnet energized also. The rotary magnet 132 then operates to rotate the sha-ft wipers into engagement .with the desired line #2220. If this line is busy at the time, the connector side switch will be locked in second position. in4 the manner to be described,l and the calling subscriber is given the busy-signahthus making it impossible to extend the calling line into connection with the called line.

Before describing the results that follow when the connector finds a busy line, the description of how aV connection is established will be completed. As soon as the line relay 128 ceases to operate for the last digit, the private magnet relay 134 denergizes, as heretofore explained, in this instance permitting the side switch to trip to third position. The result is that the side switch wipers 136, 137, 138, 139 and 140 engage the contact points 214, 215, 216, 217 and 218, respectively. When the side switch wiper 138 engages the contact point 216 a guarding potential is completed at the private wiper 127 for protecting the seized line from outside interference while the connection is established. This guarding potential extends from `ground G to t e contact point 216, thence by way of the side switch wiper 138, locking-relay springs 219 and 220 to the private wiper 127. Not only does this uarding potential prevent other connectors rom seizing the same line over multiples of the normal conductors 221, 222 and 223, but it also provides means for energizing the cut-off relay 2,24 of the line switch C', whereby the switch C is prevented from operating when the called subscriber removes his receiver 225 from the switch-hook 226. It will also be seen that when the side Iswitch passes to third position the trunkrelease conductor 194 that runs between the second-selector and the connector 1s prowhen the side switch wiper14 0 engages the .vided with guarding potential from ground G1l through the line relay springs 196a and 198, contact point 217, side switch wiper 139, release relay springs 203 and 202 to the trunk conductor 194. However, while the side switch is in first or second position a guarding potential for this trunk conductor 194 is also provided from ground G, but through the side switch wiper 139 direct. The reason for this is that the guarding potential from ground Gr11 is interruptedwhile the line relay 128 is operating, and there is some liability of some other selector similar to the second-selector F stopping on the same trunk-line. After the side switch passes to third position, however, there is no such possibility, and the potential is provided from ground G through the line relay springs, as stated, in order to expedite the release of the selectors when the calling subscriber hangs u his receiver. Of course, when the side switch wipers 136 and 137 engage their third-position contact points 214 and 215, the calling subscribers line is placed in connection with the called subscribers line over the heavy conductors shown, passing through the ringer relay springs 227 and 228 on one side, and 229 and 230, on the other side. As soon as connection is thus established the ringer relay 145 is energized ,over the circuit established oint 218, the energizing current om .ground G through the intercontact flowing rupter 144, through the back-ridge relay springs 231 and 232, ringer relay 145, conductor 233, contact point 218, side switch wiper 140, (private magnet relay 134 to the battery lea 103, thence through battery B to ground G. It will be seen that as the interruptor 144 revolves, the energizing circuit of the ringer relay 145 will be broken periodically, so as not to ring the called ysubscriber' continuously. It will be seen that each time that the ringer relay is energized the springs 228 and 230 are separated from the rin er relay springs 227 and 229, thereby brea ing the calling vline from the called line and pressing the springs 228 and 230 onto the sprin s 244 and 245, which are the l terminals of t e ringer generatorl. As a result ringing current is sent over the called line for energizing the'bell 234 while the springs 237 and 246 are in contact. -It should be explained that the connector H, like all the connectors of the two-thousand two-hundred group, may be arranged to draw its ringing current from a ringer generator I that furnishes current of such character that only the ringer 234 of the substatlon #2220 will be operated by said current; while the ringers of all other substations on the same line may be so tuned that they will not respond to the current from said generator. Similarly, the'connectors of the two-thousand three-hundred group, which are employedwhen substations of this group are called, may be arranged to draw their ringing currentfrom a ringer generator that furnishes current of such character that only ringers tuned to respond to the currentof this particular character will be operated. Likewise, the connectors of the four and one vhundred groups of the two-thousand may in turn draw their ringing current from still other generators that supply current of such character that only these ringers that are correspondingly tuned will operate. It is evident, then, that when generator current is projected out on the line by the connector H of the two-thousand two-hundred group only the ringer 234 will be operatively fftected. However, as soon as the called subscriber answers, the back-bridge relay 141 is energized by a flow of current from ground G1, contact point 216, side switch' wiper 138, winding 143 of the back-bridge relay 141, conductor 235'. ringer relay springs 229 and 230, side switch wiper 137, contact pointl 215, rotary line wiper 126, rotary normal conductor 222, rotary line conductor 236, switch-hook springs 237 and 238,'impulse springs339 and 240, transmitter 241, vertical line conductor 242, vertical normal,

thence to the battery lead 103, and through battery B to lground G. lVhen the bucle bridge relay 141. is once energized, however, the energizing circuit for the ringer relay 145 is interrupted at. a point between the springs 231 and 232, thus making it impossible for the ringer relay to energize as long as the called suliscriber is on the line. The subscribers being thus connected` they may conununicate over the main talking conductors indicated by the. heavy lilies and including on one side the condenser 117 at the connector 1-1. and on the other side the condenser 14,8. This talking;A circuit also includes the windings 21 and'22 of the double-wound coil 23. For the purpose of clearing the talking circuit of the impedance of these coils, the condeusers 247 and 24S are provided across the said windings, as shown. After the subscribers are through talking, if the calling subscriber hangs up his receiver he opens the line circuit at a Joint between the springs 17 and 1S, thereby initiating the'release of all of the switches. This release is as follows: At the instant .that the circuit is broken between the said springs 17 and 1S, the double-wound line re# lay 128 and the release relay 133 of the connector H denergize. At the instant that. the slow-acting relay 133 and the line relay 128 denergize, the energizingr circuit for the release magnet '-133 is closed at a point between the springs 199 and 200 and at another point between the springs 196a and 197. A flow of current is, therefore, set up from ground G through the springs 196a and 197, through the springs 109 and 200 to the release magnetl 133, thence through said i'n-agnet `and to the oil-normal spring 132, to the contact point 131, and to the battery lead 103, thence through battery B to ground G. The release magnet instantly rcleases the connector switch shaft and side switch, thereby breaking the energizing circuit through the back-bridge relay 141, if the called subscriber has not in the meantime restored his receiver, and also the energizing circuit through the bridge-cut-oft' relay 224 of the called line switch C. As soon as the connector switch shaft reaches its lowest position it breaks the circuit for the release magnet 133 by separating the olf-normal spring 132 from the contact point. 131. at which instant the release magnet of the connector is also restored. The operation of the line relay 123 and ot' the slo\\'acting relay 133 not. only causes the Vrelease of the. connector, as described. but

also the release of the preceding switches` because the ,ground connection from ground (ir1 to the trunkrelease conductor 104 is interrupted by both of. these relays. Since the release relays 124 and 112 are dependent upon that ground for their energized condition, as already explained, it fol lows that they will fall back, with the following results: As soon as the release relay 121 ot' the second-selector F denergizes, the spring 17T falls back into normal engagement with the spring 17S, thereby closing an energizing circuit for the release magnet 121 from ground G7 through the springs 174 and 175, and through the springs 17% and 178 to the release magnet 121, thence to the contact point 219, olf-normal spring;r 2.30 to the battery lead 103, thence through battery B to ground G. As soon as the release magnet 121 energizes, the Vsecond-selector side switch and switch shaft are restored, which latter, upon reaching its lowest position, opens up. the release circuit at a point between the off-normal spring 250 and the contact point 240, whereby the release magnet 121 is denergized. When the release relay 112 ot' the selector E denergizes, the springs 103 and 161 are brought into rontact, and as a result the energizing circuit for the release magnet 10S is closed. The energizing current for this release magnet 108 then flows from ground G through the springs 101 and 10G, and. through the said springs 1(33 and 104 to the release magnet 10S, thence thro-ugh said magnet to the contact point 110, off-normal spring 111 to the battery lead 103, thence through battery B to ground G. The release magnet, upon energizing, then restores the rst-selector'side switch and switch shaft, which latter, upon reaching its lowest position, opens the energizing circuit for the release magi-net 108 at a point between the off-normal springr 111 and contact point 110. Furthermore, when the relay 112 de-inergizes and closes the springs 163 and 164 in contact., a series energizing circuit through the release magnet 24 and the release relay 113 is established. This circuit extends from ground G through the springs 161 and 166, springs 163 and 104, through the relay 113, springs 251 and 252, conductor 77 to the bank springs 4-2 and 41, thence ,through the release magnet 24 of the line switch C to the battery lead 103, and through battery B to laround G. It will be seen that the release magnet will then enei'-,

,qize and, as previously explained, cause the trip armature 27 to fall over the plunger arm 22, whereby the. menlbers 32 and 33 engage. (See Fig. 4). As lthe release relay 113 energizes and separates the. springs 251 and 252 the series release circuit is broken for an instant, which permits the release magnet 24 of the line switch (l to denergize, thereby vvithdra\\in;r the plunger 2l from the bank terminal Q. As a result the bank springs 41 and 42, as well as the other bank springs of the line switch (l, are separated, thus preventing any other action from the trunk. After the switches aw.l thus rcstored the calling subscril'ier can; of course, then proceed to make another call.

Returning now to that stage of the c all where the calling subscriber was operating the connector switch in accordance with the last digit 0, it will be explained what takes )lace in the event that the desired line is usy. When the line #2220 is calling, or when it has been called by someone else, the private bank contacts in which the normal conductor 223 terminates are connected to ground. If another connector switch has called the line, this guarding potential Ais supplied through the connector switch from a ground terminal similar to the ground terminal G in the connector switch H, as already, explained; but if the line switch C is calling, a guarding potential is established from the trunk-line relay ground as in Fig. 1,l thence to the private bank contact. In a similar manner the line switch C protects the calling line A (when the bank springs 39 and 40 come into contact) from ground G, from which ground connection is established through the said bank springs to the private normal conductor 80. Therefore, when the subscriber sends in the last impulse the private wiper 127 is carried onto the grounded contact; and when the slowacting relay 134 of the connector' denergizes, instead of theside switch tripping to third position, as in'the case where the line is not busy, it is locked and the calling subscriber is then given the busy-signal. The method by which this side switch is locked is as follows: The slow-acting relay springs 209, 210 and 211 are so arranged that as the relay 134 denergizes, the spring 209 engages he spring 210 before it leaves the spring 211, and in this way the private magnet 135 is prevented from denergizing, be` cause the spring 210 is connected with the private wiper 127 at the time, over the following circuit: from the private wiper 127 to the locking spring 220, thence to the spring 219 and through the winding 143 of the back-bridge relay 141 to the talking line conductor 235, thence through the ringer relay springs 229 and 230 to the side switch wiper 137, contact point 253 (the side switch being in second position) to the slow-acting relay spring 210. Therefore, when the spring` 20S) engages the spring 210 the private magnet 135 is not denergizcd, since the energizing circuit is maintained from the private wiper 127 to the said spring 210, as described, thence through the spring 20S), and tl'irough the private magnet 135 to the 'battery lead 103, thence through battery B to ground G. The private magnet therefore remains energized, retaining the side switch in second position. It will be seen that at the same time the back-bridge relay 141 energizes in series with the private magnet 135, over this circuit, from the private wiper 127. Therefore, the back-bridge relay 141,

upon energizing, presses the springs 25,4 and 255 into Contact, thereby energizing the locking relay 146 over the following circuit: from ground Gr13 through the slow-actlng relay springs 211 and 212, through the private magnet springs 256 and 257, through the said relay 146, and through the backbridge relay springs 255 and 254 to the battery lead 103, thence through battery B to ground G. It will be seen that when `the relay 146 energizes, the connection between the rotary magnet 132 and the battery lead 103 is broken at a point between the springs 21'1 and 212. The object of this arrangement is to prevent the calling subscriber from further rotating the connector switch if he should attempt to `operate his dial while receiving the busy-signal-that is, while the connector switch is locked in second position. It will also be seen that when the relay 146 energizes, the circuit for maintaining the private magnet 135 energized is shifted from the private wiper 127 to the spring 258, which latter is connected to ground G1". The object of this arrangement is to prevent the side switch from unlockin'f and passing to third position, if theswitch that is maintaining the called line busy should be released while the calling subscriber A (Fig. 1) is receiving the busy-signal. It will be evident that if the ground Gr19 were not substituted for the ground at the private wiper 127, the private magnet 135 would denergize if the switch that is supplying' ground at the -private wiper 127 should release, which would, of course, be undesirable. It will also be seen that the relay 146, upon energizing, closes the springs 259 and 153 in contact, thereby establishing the busy circuit as follows: from the secondary winding of the busy c oil 151 through the springs 153 and 259 to the second-position side switch contact point 260, side Switch.

wiper 136, ringer relay springs 228 and 227, through the condenser147, through the substation A to the rotary side of the line, then over said rotary side back to the connector H, through the winding 130 of the line relay 128 to ground Gr1 to the interrupter round G20, through the interruptor 149 to te primary winding of the busy coil 151 back to the secondary winding. When the calling subscriber receives the busy-signal he understands that the line is busy and hangs up his receiver. The line circuit is opened, as already explained, with the result that the line and slow-acting relays 128 andI 133 of the connector H denergize, causing the release of the connector and all othe;` switches, as heretofore explained. It will, of course, be seen that as soon as the side switch is restored the energizing circuit for the backibridge relay 141 that includes the winding 143 thereof, and for the private magnet 135,

, Station A ,whose number Y the spring i be uuliir..

is broken when the side switch wiper 137 leaves the contact point 253. Now, since the enei'gizin circuit for the locking relay 1516 is contro ed by the back-bridge relay 141, the said locking relay salso Vdenergized, and the connector switch is left in a. normal condition.

In the foregoing it has beenshown how a subscriber' vmay ,operate the central oliice switches to establish connection with an other line. It will now be 'ointecl out how a subscriber may operate t e central office apparatus to call and signal' a party on the same line This in ay be moieclearly under- -stood from an ex lanation' of Fig. 3 when it is assumed that t e subscriber at substation A desires to signal the subscriber at subis 5320. To call this number the substation dialis operated in the usual manner. When' the line switch operates to seize a trunk-line leading .to a first-se1cctor.s\ viteh,a guarding potential is established at the connector bank throu h the trunkflin'c relay springs, as previous y explained. The master switch D operates as usual to' carry the idle plunffers opposite the next available trunk-line. l`lie impulses for the first digit 5 are received by the firstseleetor switch E, which operates to select an idle trunk-line leading to a second-selector F. The second-selcctor responds for. the second digit Bite-select a connector switch H of the ftythrce-hundrcd group. `his connector is operated by tho last two digit impulses to select the li'ne number QQ'of this` roup. The-usual guarding potentials are established to protect the various trunklines used .in establishin the' connection. As previously explained, t ie tiiink-li`ne relay 23* operates when the impulses are transmitted. The operation of this relay is of no Vii'riportanee until this particular time-that is, when a subscriber i'sahout tooperate a connector switch to'call back on his own line.

This relay is provided tor temporarily removing thoyg'gua'rdin'g potential from the connector banks, so that the connector switch l-l will not find the line busy. The o era.- t'ion of the tiiink1ine relay 23 is as fol ows; 'hen the. impulscsarc transmitted the relay 23' dciiueigzes at'each impulse1 permitting lit" 'to engage the spi-ing 20 momentarily. The engagement ofthese two springs provides an 'enel-,agizingv circuit for the slow acting relay l5 trom 4ground "'th-rougli the said relay, :spi-ings 20* and Ill, bank springslfi() a-iul 3%), through the windiugof the liridge-cllt-olt' relay 48 to the hatterylcad 10i-l. thence through battery yB lo ground (l. The relay l5" thcrcul'ion energizes and separates (he springs lh" and1 17",

whercliy the guarding' polen( ml 'for thc no r mals orga-inhbil@ ,line is removed. .It will ood, of course, that 'while the .said rela inan `o erated .Subscribers transmitter is overcome, an

relay 23 enerizes and denergizes during each impulse, eslow-actiii relay 15 does .not2 since the intermittent c using of" its enf ergizinc circuit is suicient to maintain the osition. After the impu ses are de ivered tlh mains in an energized position maintaining the guarding potential at t e connector bank. From the foregoing it will .be seen that while impulses are being transmitted,4 the protecting potential of the line is teml por-.ii-il)r removed. When the connector switch is operated for ther'lastdigit OJtheconnector side switch does notlock in second'.

position, but passes to third position, establishing connection with the Adesired lino.`

The subscriber at substation A having opperatcd the central office switches k a rstfselcctor, second-selecteren connector switch H, to call subscriber A. on' his own line, now presses the signaling button -5 in 'order that .theringer generator may. jbe

that the back-bridge relay 141 energized' when the called subscriber answered and bridged his transmitter across the line." In

this instance (the called andcallinglines being identical.) a provision .is niadefwhelef-v the ell'ect of the' bridge of the calling.

d the including back-bridge relay'14l denergized to-pcrmit l the closing,lr of the energizing'circuit through the ringer relay 145, as follows: When the button 5" is pressed the springs 6 and 7.*

dsengage, introducing the high resistance coil S into the circuit lof the back-bridge relay 14.1 and the 'front-bridge line rela Y 128. "When the resistance coil 8 is place ei'giz/.ed position.

ing the circuit through the ringer relay 145,'

as irevionsly. However, sutiicient-current its energized position. and thus prevent a, i

premature release of the switches. When the subscriber at substation A answers by removing the receiver from the switch-hook and bridging liis'transinitter across eoiuhictors, a new circuit is formed-which, shunts the resistance coil 8". The relay. 141

n ow eneifpizes, hreakingthe circuit of the, i

The-two suhstationsA ringer re 1y llefi. and battery current for talking puioses being the-line' p are thus placed in. communication,

lcd in the usual manner lt rough the lincrelay 128 and the baelb'bridge relay 141.

in this. circuit sullicient current d oes not How to'maintain the back-bridge relay-iii'an 'en' Hence itfalls back, closstil flows to maintain the line relay 12B=n nl! When the subscribers are through talking, the last one who restores his receiver 'to its switch-hook initiates the release of the central office switches in the usual manner, as explained.

By referring to Fig. 6 a clearer understanding may be obtained of the arrangement by which the ditferent substations may be signaled selectively. In said figure are shown a number' of groups of lines, each of which is rovided with three substations (A2, A an A4) and connected to an individual or line switch. From the line switch groups trunks lead to first selector switches, from which latter switches trunks lead to second selector switches. From the second selectors trunks lead to connector switches. In this diagram the switches and substations are represented by circles and the different levels of bank contacts are represented by straight lines. It will be assumed that the substations A, A2 and A3 are numbered 2120, 2220 and 2320, respectively. Since the last two digits of each of these numbers are 20, the line to which these substations are connected would be connected to the last or O contact in the second level in each ofthe three groups of connectors I-I, H and H2. Each group of connectors is connected to a different generator, I, I or I2, each having a dierentfrequency. Since the group of connectors H2 is connected to the first. level of the second selector banks, the connection with the called line will be completed by one of these connectors if the number 2120 is called. Ringing current will then be supplied by the generator I2, which is of the .proper frequency to actuate only the bells at substation A. If number 2220 is called the connection will be completed by one of thc connectors H, and ringing current will be furnished by generator 1, which is of the proper frequency to signal substation A2. Likewise, a connection for substation #2320 will be completed by the connector H and ringing current supplied by generator I.

From the foregoing it will'be seen that I provide ciicicnt party-line service in a twowire autolnatic telephone exchange systemtlhat is to say, in a system in which the subscribers lines are free from operating grounds outside ot the exchange or central station. It will also be secu that I provide a twowire automatic Asystem in which party-line subscribers can signal each other on thc same liuc. through the medium of push-buttons at their respective stations, whereas any called subscriber who is not on the same line with the calling subscriber is automatically signaled from the exchange or central station. Furthermore, I provide a two-wire automatic system in which the connectors are capable of automatically locking on busy lines, Without closing the connection from the calling line to the called line, the subscriber on the calling line being given a busy signal.Y Also, and through the medium of the slow-acting relays 48 and 15 and the double-wound line relay 23, a two-wire party-line subscriber can call back on his own line for the purpose of establishing telephonie communication with another subscriber on the same line. Thus Iprovide improved two-wire service in an automatic exchange, and in addition I provide party-line service in a two-Wire trunking system. In connection with this system it will be understood that wheneyer I use the word trunking I mean any opera-AI tion that carries the calling line nearer the called line. For example, 1n the connector switch I consider for the purposes of this application the first operation of the connector switch as a trunking operation.

What I claim as my invention is 1. In a telephone system, subscribers lines, each substation having a calling mechanism operative in response to manual operation thereof to transmit current for one digit of the called number and then come to rest before further manual operation -for the next digit, means for extending connection to a called line by using the two sides of the calling line in series, a plurality of substations on the called line, means for selectively ringing the different substationsy on the partyine, saidl first means comprising a trunk selector individual to the calling line, trunk lines accessible to said selector, and means for said trunk selector responsive to perform the first trunking operation of the selector in response to the closure of both sides of the calling line in series to reject busy trunks and to select an idle trunk independent of any further action from the line.

2. In a telephone system, subscribers lines, cach substation having a calling-mechanism operative in response to manual operation thereof t0 transmit current for one digit of the called number and then come to rest before further manual operation for the next digit. means responsive to the current corresponding to a plurality of digits'o'f the called number for extending connection to a called line by using the .two sides of' the calling line in Series, a plurality of substations on the calling line, means for releasing controlled from any calling substation on the party-line, said first means com rising a trunk selector individual to the cal ing line, trunk lines accessible to said selector, and means for said trunk selector responsive to perform the first trunking operation of the selector in response to the closure of both Sides of thecalling line in series to reject busy trunks and to select an idle trunk independent of any further action from the line.

anothersubstation on finatie means for ringing a substation oiia line other thanvthe calling line.

l.v A4 two-wire selective ringing party-line automatic telephone exchange system free from operating grounds outside of theex change or central station, 'a plurality of lilies, a substation for eiieli'- line, means for connecting any twolines, said meanscomprising a trunk selector individual to the 'calling line.

selector. and nieaus for said trunk selector responsive to perform the first truultiug operation of the selector in response to the clof sureof both sides of tli'e calling line in series to reject busy trunks and to select an idle trunk, independent of any further action froin't'heline, each substation haring a calling mechanism operative iii'response to maninit operation thereofl to transmit current for our. digit of the called number and'thcii come to rest before furtheninaninil operation for the next digit.

6. A party-line automatic telephone exchange system having release mechanism, and a high resistance. at cach substation ou thepartydiiie to prevent arcleaSe when one siiliscrilior signals 'another on the saine line. 7. In u telephone systcui. a ringingl key, au automatic subscriber-s lino provided at. the substation tlicreofwitli ul higliresistaiice ooill normally sliortlc'ircui'ted by lthc closed contacts of the ringingY key.A `8. Ina tclcphoiii` systcui. a ,ringing key, an automatic suhsrrib'ci"svliuc( iiirans for automatically ixtcndiner connection thorefro-ni by usine tlictwo sides thereof in soiics, u'ud :i resistance coill in thc line at the substation thereof normally short-circuitcd by tliocloscil contacts of the ringing key.

S). lii'a telri-ihoue system. trunks for con ncction with calling;lines;subscribers lincsu' lucana for automatically cxtciulingf,r connection toV a 'called liuc b v usingthc. two sides of tho calling liuc in scrcs. a slo'ir-ucting.'u biidjleazut-oll relay lFor carb liuc. and a doul|lc\\'oiunl relay and a sloiruirling, relay for cacfli tinuk'lo u'hirh calling liiicscan be dirortlr conoci-tod. as scl forth.

l0. lu a tolcphuuc s vslrni including partyl linisa. trunks for connection li||cs'.-iiiraiis loi'fciiabling u subscriber to call comprising a slow-acttriink lilies accessible to said ,come to rcstbefore further manual operation for the next digit, trunlorelea-se;cir'

loli` relay. a bridge on Said cuit through with cnllliig ing reiayrindividanto uit 'party-nat, niet slow-actin relay and another relay for each trunk to' w ich the pu rty-'li-ue can be directly connected, as set forth.

11. 'In a telephone system','.th'ombinaf tion ot a party-line having a` pluralityI of substations thereon, means for automatically extending connection therefrom. by

using the two sides of the line in-scres, each, ine iauism opl' substation having n, calling erative in response to manual eration thereof.- to transmit current'fo'r ne digit.y

ofithe called number and then cometo rest -beforel f urtlicr manual operation for' the next digit, truuka'eleasei circuits, means for` the line. circuits,

initiating the release over a truuk selector said' first means 'comprising individual to the calling line, accessible to said selector aiid-nie'i'i'is for said trunk selector responsive. trunlringo eration of the selector iiirespense 'to l. ie closure ofl bot-h sides of the to perfornitlie first trunk lines calling-line in series to reject busy trunksand to select an'V idle trunk in dcpendent'ot any fui-'ther action from the liner' Iii a telephone system, tion of a partyline having a pluralityoi substations thereon,

the combinameans for antoiiiiiti-y cally extending connection therefrom.' by

sides ofthe callingI line-y in using the two mechanism operative iii 'response to series, each substation having ,a callin y anuafj operation thereof to transmit-,currei'i'tfqr one digit of the. called' number andt-lienk ico cuits provided with slowiicting releas'ere 4 lays, and means for initiating the release over the line circuits.

13. A suhscribcrs telephone line free'fron I 'operating grounds outside of the exchange or central station 'ii-nd provided with afsloilYf.

acting bridge-cubed relay and a bridge normally closed through the contacts thereof;

14| a subscribers telephone line free from operating grounds outside of the exhaii e` or central station, a slow-acting bridge-cu closed through the contacts" telephone ero for lorliina` oiia. husy'lineV line normally oi'saidrclamn trunk, a loiible\.\'oiiiid line relay and a slow-"' i acting relay for said trunk, and two cir vcuits for the first slow-actiug relay, onecirthe winding of the second slows A' li theconf-.l

las

transmit 'current ,for one 

